Remember Slash doesnt play that riff as chords when he plays it live. And on the record its double tracked with him and izzy playing it.
I doubt it was recorded as a chord riff, I think they just recorded different tracks of it in the various positions.
Its not easy to play as chords but keep practicing. I remember I found For Whom the Bell Tolls difficult, that has a fast chordy riff at the begining, but it becomes second nature after time.